1. Field of the Invention
The present invention relates to an oscillator and a communications device in which a circuit board and a resonator and the like are stored in a package.
2. Description of the Related Art
By way of background, an example of an oscillator will be discussed as shown in FIGS. 6 and 7, it being understood that this oscillator was not known at the time of the present invention and, therefore, is not prior art to the instant application. FIG. 6 is an exploded perspective view of the oscillator, and FIG. 7 is a cross-sectional view taken along the line Z--Z of FIG. 6.
As shown in FIGS. 6 and 7, oscillator 110 comprises a package 111, a case 130, a resonator 120 and a circuit board 140. The package 111 comprises a steel cap 112 and a stem 113. Terminal pins 114 are provided at three corners of the stem 113. The case 130 has a two-level concave portion 131 in its center, and is provided on top of the stem 113. The resonator 120 comprises an electrode 122, which is provided on two opposing faces of a dielectric substrate 121, and a substantially circular electrode removal portion 123 is provided roughly in the center of the electrode 122. Furthermore, the electrode 122 is also provided on the four side faces of the dielectric substrate 121. The resonator 120 is held in the concave portion 131 of the case 130, and the two-level structure of the concave portion 131 creates a space near an electrode removal portion 123 in the bottom face of the resonator 120.
The circuit board 140 comprises a circuit pattern, such as a stripline, provided on an insulated substrate 141. A FET 142, a varactor diode 152, a chip capacitor 143 and chip resistors 144a, 144b and 144c and the like are provided at predetermined positions on the substrate 141. The circuit board 140 is mounted on the case 130, and terminal electrodes 149, 150 and 153 of the circuit board 140 are connected to the terminal pins 114.
The case 130, with the resonator 120 therein, is placed on the stem 113 and the circuit board 140 is mounted on the case 130. Thereafter, a cap 112 is provided over the assembly. The cap 112 is hermetically sealed to the stem 113, forming the oscillator 110.
The characteristics of an oscillator are greatly affected by the relative positions of the resonator and the circuit board or the cap. That is, when the positions of the resonator and the cap change, the distribution of the electromagnetic field changes, greatly affecting the characteristics of the oscillator. This effect is particularly noticeable at high-frequency bands such as microwave and milliwave bands, which require positioning with precision of below 0.1 mm.
Therefore, in order to obtain the desired characteristics, it is necessary to repeatedly measure the characteristics of the oscillator while adjusting the relative position. Each time, the cap and the circuit board are removed and the position of the resonator is altered. Then, the circuit board is remounted and the cap is replaced.
However, some deviation in position of the cap inevitably occurs each time the cap is replaced. Consequently, when the cap is removed and the position of the resonator and the like is altered, the deviation in the position of the cap thereafter changes the distribution of the electromagnetic field, making it difficult to measure characteristics of the oscillator appropriately and with stability. Furthermore, due to the deviation in the position of the cap, the path of a ground electrode from the cap to the stem is also unstable, affecting the characteristics of the oscillator.